Process for hydrogenating carboxylated nitrile rubber, the hydrogenated rubber and its uses

ABSTRACT

Polymers of a conjugated diene, an unsaturated nitrile and an α,β-unsaturated carboxylic acid are selectively hydrogenated to reduce carbon-carbon double bonds, without also reducing carboxyl groups and nitrile groups, using a rhodium-containing compound as catalyst. The hydrogenated polymers are novel and display excellent adhesive properties at both room temperature and high temperature, excellent hot tear strength, and excellent abrasion resistance.

FIELD OF THE INVENTION

The present invention relates to novel polymers to processes forpreparing them, and to their uses.

BACKGROUND OF THE INVENTION

There are known polymers of conjugated dienes and unsaturated nitrites,i.e. nitrile rubbers. It is also known to hydrogenate these. Thisimproves the heat-aging properties of the polymer. When doing so care isneeded to ensure that only hydrogenation of carbon-carbon double bondsoccurs. Hydrogenation of the nitrile moieties is to be avoided, as anyreduction of the nitrile groups has an undesired and deleterious effecton the properties of the nitrile rubber; in particular it reduces theoil resistance of the nitrile rubber.

It has been proposed to include various additional copolymerisablemonomers in nitrile rubbers. Among the copolymerisable monomersmentioned are α,β-unsaturated mono- and dicarboxylic acids. These can beincorporated into the polymer backbone, but difficulty has beenencountered when polymers containing carboxyl groups have beenhydrogenated. Particularly if the degree of hydrogenation is high, thecarboxyl groups have undergone reduction or other side reactions, whichhas resulted in an unsatisfactory product.

To avoid the problem of hydrogenation of the carboxyl groups it has beenproposed to prepare a nitrile rubber composed of a conjugated diene andan unsaturated nitrile, to partially hydrogenate this nitrile rubber andthereafter to add α,β-unsaturated acid; see U.S. Pat. No. 5,157,083.This approach has not proven satisfactory. As the acid is added afterthe formation of the nitrile rubber the acid moieties are notdistributed randomly nor alternately along the backbone of the polymer.Terpolymerisation of a conjugated diene, unsaturated nitrile andunsaturated acid results in a polymer in which the α and β carbon atomsof the acid form part of the main carbon backbone of the polymer. Incontrast, polymerisation of conjugated diene and nitrile results in apolymer that has some carbon-carbon double bonds in a vinyl side chain,from 1,2-polymerisation of butadiene, and some carbon-carbon doublebonds in the main polymer backbone, from 1,4-polymerisation ofbutadiene. These double bonds in the main polymer backbone may be in thecis or in the trans configuration. When the polymer undergoeshydrogenation the vinyl groups undergo hydrogenation first, followed bythe double bonds in the cis configuration. Hence, the partiallyhydrogenated polymer to which the α,β-unsaturated acid is added containsmostly or entirely double bonds in the main polymer backbone and in thetrans configuration. Reaction with the unsaturated acid results in aproduct in which the α and β carbon atoms of the acid are not in themain carbon backbone of the polymer. Hence, the chemical structure of apolymer made in this latter way differs from the chemical structure ofthe statistical polymers that is formed by the terpolymerisation of aconjugated diene, an unsaturated nitrile and an unsaturated acid, wherethe monomers are statistically or randomly distributed throughout thepolymer chain.

European Patent Application No. 933381 is concerned with carboxylatednitrile-group-containing highly saturated copolymer rubber, and in theBackground Art discusses three processes for adding maleic anhydride toa nitrile-group-containing highly saturated copolymer rubber. TheEuropean application refers to “a highly saturated copolymer rubber”,but it is believed that some degree of unsaturation in the rubber isrequired, to serve as reaction sites for addition of the maleicanhydride. Disadvantages of all three processes for adding maleicanhydride are mentioned, and it is said that no satisfactory industrialprocess has been found. Furthermore, the product of the addition, i.e.,the maleic anhydride-nitrile-group-containing polymer is said to beunsatisfactory in various properties, including “abrasion resistance andtensile strength which are required for belts and hoses.”

Preparing a carboxylated, hydrogenated nitrile rubber by first preparinga nitrile rubber, then hydrogenating and thereafter adding anunsaturated acid results in an expensive production process.Furthermore, it is difficult to control the amount of acid that adds tothe polymer so the quality of the product is uncertain. A product madein this way was introduced commercially but has since been withdrawnfrom the market.

SUMMARY OF THE INVENTION

A process has now been discovered that permits the selectivehydrogenation of a polymer whose backbone is composed of a conjugateddiene, an unsaturated nitrile and an unsaturated carboxylic acid, anddoes not result in any detectable hydrogenation of nitrile or carboxylmoieties. This permits the preparation of a novel polymeric materialthat is a hydrogenated polymer of a conjugated diene, an unsaturatednitrile and an unsaturated acid. It has also been found that this novelpolymeric material has unexpected and valuable properties.

Accordingly, in one aspect, the present invention provides a polymer ofa conjugated diene, an unsaturated nitrile and an unsaturated carboxylicacid that has been selectively hydrogenated to reduce carbon-carbondouble bonds without hydrogenating nitrile groups and carboxyl groups.

In another aspect, the present invention provides a process forselectively hydrogenating a polymer of a conjugated diene, anunsaturated nitrile and an unsaturated carboxylic acid which comprisessubjecting the polymer to hydrogenation in the presence of arhodium-containing compound as catalyst and a co-catalyst ligand,wherein the weight ratio of the rhodium-containing compound to theco-catalyst ligand is from 1:3 to 1:55.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a graph, which shows the infrared spectrum of the polymerprior to and subsequent to hydrogenation.

FIG. 2 shows a graph, which shows the degree of hydrogenation achievedwith different amounts of ligand co-catalyst.

FIG. 3 shows a graph, which shows the degree of hydrogenation of apolymer with time using various different amounts of catalyst loading.

FIG. 4 shows a bar chart, which shows die B tear strength of HNBR, XNBRand HXNBR compounds at different temperatures.

FIG. 5 shows a bar chart, which shows die C tear strength of HNBR, XNBRand HXNBR compounds at different temperatures.

FIG. 6 shows a bar chart, which shows the adhesion to nylon of HNBR,XNBR and HXNBR compounds at room temperature and at 1250° C.

FIG. 7 shows a bar chart, which shows results obtained with HNBR, XNBRand HXNBR in the Pico abrasion test; and

FIG. 8 shows a graph of storage tensile modulus E′ versus temperaturefor HNBR, XNBR and HXNBR.

DESCRIPTION OF PREFERRED EMBODIMENTS

Many conjugated dienes are used in nitrile rubbers and these may all beused in the present invention. Mention is made of 1,3-butadiene,isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene and piperylene, ofwhich 1,3-butadiene is preferred.

The nitrile is normally acrylonitrile or methacrylonitrile orα-chloroacrylonitrile, of which acrylonitrile is preferred.

The α,β-unsaturated acid can be, for example, acrylic, methacrylic,ethacrylic, crotonic, maleic (possibly in the form of its anhydride),fumaric or itaconic acid, of which acrylic and methacrylic arepreferred.

The conjugated diene usually constitutes about 50 to about 85% of thepolymer, the nitrile usually constitutes about 15 to 50% of the polymerand the acid about 0.1 to about 10%, preferably 0.5 to 7%, thesepercentages being by weight. The polymer may also contain an amount,usually not exceeding about 10%, of another copolymerisable monomer, forexample, an ester of an unsaturated acid, say ethyl, propyl or butylacrylate or methacrylate, or a vinyl compound, for example, styrene,α-methylstyrene or a corresponding compound bearing an alkylsubstitutent on the phenyl ring, for instance, a p-alkylstyrene such asp-methylstyrene. The polymer preferably is a solid that has a molecularweight in excess of about 60,000, most preferably in excess of about100,000.

The polymer that is to be hydrogenated can be made in known manner, byemulsion or solution polymerisation, resulting in a statistical polymer.The polymer will have a backbone composed entirely of carbon atoms. Itwill have some vinyl side-chains, caused by 1,2-addition of theconjugated diene during the polymerisation. It will also have doublebonds in the backbone from 1,4-addition of the diene. Some of thesedouble bonds will be in the cis and some in the trans orientation. Thesecarbon-carbon double bonds are selectively hydrogenated by the processof the invention, without concomitant hydrogenation of the nitrile andcarboxyl groups present in the polymer.

The selective hydrogenation can be achieved by means of arhodium-containing catalyst. The preferred catalyst is of the formula:(R_(m)B)₁RhX_(n)in which each R is a C₁-C₈-alkyl group, a C₄-C₈-cycloalkyl group aC₆-C₁₅-aryl group or a C₇-C₁₅-aralkyl group, B is phosphorus, arsenic,sulfur, or a sulphoxide group S=0, X is hydrogen or an anion, preferablya halide and more preferably a chloride or bromide ion, 1 is 2, 3 or 4,m is 2 or 3 and n is 1, 2 or 3, preferably 1 or 3. Preferred catalystsare tris-(triphenylphosphine)-rhodium(I)-chloride,tris-(triphenylphosphine)-rhodium(III)-chloride andtris-(dimethylsulphoxide)-rhodium(III)-chloride, andtetrakis-(triphenylphosphine)-rhodium hydride of formula ((C₆H₅)₃P)₄RhH,and the corresponding compounds in which triphenylphosphine moieties arereplaced by tricyclohexylphosphine moieties. The catalyst can be used insmall quantities. An amount in the range of 0.01 to 1.0% preferably0.03% to 0.5%, most preferably 0.06% to 0.12% especially about 0.08%, byweight based on the weight of polymer is suitable.

The catalyst is used with a co-catalyst that is a ligand of formulaR_(m)B, where R, m and B are as defined above, and m is preferably 3.Preferably B is phosphorus, and the R groups can be the same ordifferent. Thus there can be used a triaryl, trialkyl, tricycloalkyl,diaryl monoalkyl, dialkyl monoaryl diaryl monocycloalkyl, dialkylmonocycloalkyl, dicycloalkyl monoaryl or dicycloalkyl monoarylco-catalysts. Examples of co-catalyst ligands are given in U.S. Pat. No.4,631,315, the disclosure of which is incorporated by reference. Thepreferred co-catalyst ligand is triphenylphosphine. The co-catalystligand is preferably used in an amount in the range 0.3 to 5%, morepreferably 0.5 to 4% by weight, based on the weight of the terpolymer.Preferably also the weight ratio of the rhodium-containing catalystcompound to co-catalyst is in the range 1:3 to 1:55, more preferably inthe range 1:5 to 1:45. The weight of the co-catalyst, based on theweight of one hundred parts of rubber, is suitably in the range 0.1 to33, more suitably 0.5 to 20 and preferably 1 to 5, most preferablygreater than 2 to less than 5.

A co-catalyst ligand is beneficial for the selective hydrogenationreaction. There should be used no more than is necessary to obtain thisbenefit, however, as the ligand will be present in the hydrogenatedproduct. For instance triphenylphosphine is difficult to separate fromthe hydrogenated product, and if it is present in any significantquantity may create some difficulties in processing of the product.

The hydrogenation reaction can be carried out in solution. The solventmust be one that will dissolve carboxylated nitrile rubber. Thislimitation excludes use of unsubstituted aliphatic hydrocarbons.Suitable organic solvents are aromatic compounds including halogenatedaryl compounds of 6 to 12 carbon atoms. The preferred halogen ischlorine and the preferred solvent is a chlorobenzene, especiallymonochlorobenzene. Other solvents that can be used include toluene,halogenated aliphatic compounds, especially chlorinated aliphaticcompounds, ketones such as methyl ethyl ketone and methyl isobutylketone, tetrahydrofuran and dimethylformamide. The concentration ofpolymer in the solvent is not particularly critical but is suitably inthe range from 1 to 30% by weight, preferably from 2.5 to 20% by weight,more preferably 10 to 15% by weight. The concentration of the solutionmay depend upon the molecular weight of the carboxylated nitrile rubberthat is to be hydrogenated. Rubbers of higher molecular weight are moredifficult to dissolve, and so are used at lower concentration.

The reaction can be carried out in a wide range of pressures, from 10 to250 atm and preferably from 50 to 100 atm. The temperature range canalso be wide. Temperatures from 60 to 160°, preferably 100 to 160° C.,are suitable and from 110 to 140° C. are preferred. Under theseconditions, the hydrogenation is usually completed in about 3 to 7hours. Preferably the reaction is carried out, with agitation, in anautoclave.

Hydrogenation of carbon-carbon double bonds improves various propertiesof the polymer, particularly resistance to oxidation. It is preferred tohydrogenate at least 80% of the carbon-carbon double bonds present. Forsome purposes it is desired to eliminate all carbon-carbon double bonds,and hydrogenation is carried out until all, or at least 99%, of thedouble bonds are eliminated. For some other purposes, however, someresidual carbon-carbon double bonds may be required and reaction may becarried out only until, say, 90% or 95% of the bonds are hydrogenated.The degree of hydrogenation can be determined by infrared spectroscopyor ¹H-NMR analysis of the polymer.

In some circumstances the degree of hydrogenation can be determined bymeasuring iodine value. This is not a particularly accurate method, andit cannot be used in the presence of triphenyl phosphine, so use ofiodine value is not preferred.

It can be determined by routine experiment what conditions and whatduration of reaction time result in a particular degree ofhydrogenation. It is possible to stop the hydrogenation reaction at anypreselected degree of hydrogenation. The degree of hydrogenation can bedetermined by ASTM D5670-95. See also Dieter Brueck, Kautschuk+GummiKunststoffe, Vol 42, No 2/3 (1989), the disclosure of which isincorporated herein by reference. The process of the invention permits adegree of control that is of great advantage as it permits theoptimisation of the properties of the hydrogenated polymer for aparticular utility.

As stated, the hydrogenation of carbon-carbon double bonds is notaccompanied by reduction of carboxyl groups. As demonstrated in theexamples below, 95% of the carbon-carbon double bonds of a carboxylatednitrile rubber were reduced with no reduction of carboxyl and nitrilegroups detectable by infrared analysis. The possibility exists, however,that reduction of carboxyl and nitrile groups may occur to aninsignificant extent, and the invention is considered to extend toencompass any process or production in which insignificant reduction ofcarboxyl groups has occurred. By insignificant is meant that less than0.5%, preferably less than 0.1%, of the carboxyl or nitrile groupsoriginally present have undergone reduction.

To extract the polymer from the hydrogenation mixture, the mixture canbe worked up by any suitable method. One method is to distil off thesolvent. Another method is to inject steam, followed by drying thepolymer. Another method is to add alcohol, which causes the polymer tocoagulate.

The catalyst can be recovered by means of a resin column that absorbsrhodium, as described in U.S. Pat. No. 4,985,540, the disclosure ofwhich is incorporated herein by reference.

The hydrogenated carboxylated nitrile rubber (HXNBR) of the inventioncan be crosslinked. Thus, it can be vulcanized using sulphur orsulphur-containing vulcanizing agents, in known manner. Sulphurvulcanization requires that there be some unsaturated carbon-carbondouble bonds in the polymer, to serve as reactions sites for addition ofsulphur atoms to serve as crosslinks. If the polymer is to besulphur-vulcanized, therefore, the degree of hydrogenation is controlledto obtain a product having a desired number of residual double bonds.For many purposes a degree of hydrogenation that results in about 3 or4% residual double bonds (RDB), based on the number of double bondsinitially present, is suitable. As stated above, the process of theinvention permits close control of the degree of hydrogenation.

The HXNBR can be crosslinked with peroxide crosslinking agents, again inknown manner. Peroxide crosslinking does not require the presence ofdouble bonds in the polymer, and results in carbon-containing crosslinksrather than sulphur-containing crosslinks. As peroxide crosslinkingagents there are mentioned dicumyl peroxide, di-t-butyl peroxide,benzoyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)-hexyne-3 and2,5-dimethyl-2,5-di(benzoylperoxy)hexane and the like. They are suitablyused in amounts of about 0.2 to 20 parts by weight, preferably 1 to 10parts by weight, per 100 parts of rubber.

The HXNBR can also be crosslinked via the carboxyl groups, by means of amultivalent ion, especially a metal ion, that is ionically bound tocarboxyl groups on two different polymer chains. This may be done, forexample, with zinc, magnesium, calcium or aluminum salts. The carboxylgroups can also be crosslinked by means of amines, especially diamines,that react with the carboxyl group. Mention is made ofα,ω-alkylenediamines, such as 1,2-ethylene diamine, 1,3-propylenediamine, and 1,4-butylene diamine, and also 1,2-propylene diamine.

The HXNBR of the inventioned can be compounded with any of the usualcompounding agents, for example fillers such as carbon black or silica,heat stabilisers, antioxidants, activators such as zinc oxide or zincperoxide, curing agents co-agents, processing oils and extenders. Suchcompounds and co-agents are known to persons skilled in the art.

The hydrogenated carboxylated nitrile rubbers of the invention displayexcellent adhesive properties and, especially, excellent hot tearstrength that is much better than that of non-carboxylated nitrilerubber. The rubbers of the invention also display better heat ageingresistance and better low temperature flexibility than non-hydrogenatedcarboxylated nitrile rubber. They also display excellent abrasionresistance, and good adhesion at both low and high temperature. Theseproperties render them valuable for many specialised applications, butparticular mention is made of use as seals in situations where severestress is encountered, high stiffness automative belts, roll covers, andhoses.

The HXNBR of the invention displays good adhesion to materials,including fabrics, woven and non-woven, metals and plastics, especiallyplastics with polar groups. The HXNBR will adhere to fabrics of naturalfibers, for example wood, cotton, hemp, silk, to synthetic fibers, forexample polyamides, polyesters, polyolefins such as polyethylene andpolypropylene, poly(meth)acrylonitriles and aramid fibers. It will alsoadhere well to glass fibers and steel cords. The HXNBR displaysparticularly good adhesion when the substrate to which it is appliedalso bears polar groups. A particularly surprising and valuable featureof HXNBR is that the good adhesion is maintained at elevatedtemperature, whereas hydrogenated nitrile rubber (HNBR) and carboxylatednitrile rubber (XNBR) both display good adhesion at room temperature butless good adhesion at elevated temperature. These properties render theHXNBR particularly valuable in applications, for example belts, where apolymer coating material is affixed as an impregnant and cover of fabricmaterial, especially for any application where the belt may encounterheat.

Hydrogenated nitrile rubber are used in many specialised applicationswhere difficult conditions are encountered. Hydrogenated carboxylatednitrile rubbers of this invention have physical properties that aresuperior in some respects to those of commercially availablehydrogenated nitrile rubbers and hence are useful in many applicationswhere hydrogenated nitrile rubbers are of proven utility. Mention ismade of seals, especially in automotive systems and heavy equipment andany other environment in which there may be encountered high or lowtemperatures, oil and grease. Examples include wheel bearing seals,shock absorber seals, camshaft seals, power steering assembly seals,O-rings, water pump seals, gearbox shaft seals, and air conditioningsystem seals. Mention is made of oil well specialties such as packers,drill-pipe protectors and rubber stators in down-hole applications.Various belts, hoses and mountings provide demanding environments andthe properties of HXNBR of this invention render it suitable forapplications in air conditioning hoses, camshaft drive belts, oil-coolerhoses, poly-V belts, torsional vibration dampeners, boots and bellows,chain tensioning devices, overflow caps and power steering hoses. Thehigh modulus and high abrasion resistance of HXNBR renders it useful forhigh-hardness roll applications in, for instance, metal-working rolls,paper industry rolls, printing rolls, elastomer components for looms andtextile rolls. The good abrasion resistance and good adhesion to metalsof HXNBR renders it suitable for use in bearing pads attached to tracksof tracked vehicles such as bulldozers and other large items of earthmoving equipment, military tanks, and the like.

The material to which the polymer of the invention is to adhere may besubjected to treatment to enhance bonding before being contacted withthe polymer. For instance, cotton rayon or nylon may be dipped in amixture that is composed of an aqueous solution of an initial condensateof resorcinal and formaldehyde (referred to as RF) and a rubber latex,this mixture being referred to as RFL. The rubber latex is notparticularly limited but may be an acrylonitrile/butadiene copolymerlatex, and acrylonitrile/butadiene/methacrylic acid copolymer latex, anacrylonitrile/butadiene/acrylic acid copolymer latex or anacrylonitrile/butadiene/vinylpyridine copolymer latex. The HXNBR rubberof this invention can be used in a latex to serve as the rubber latexfor this purpose.

Polyester and aromatic polyamide fibers may be treated with a dipcontaining an isocyanate, ethylenethiourea or epoxy, heat-treated, andthen subjected to treatment with RFL.

As indicated above, the HXNBR rubber can be used in the form of a latex.Formation of a latex can be carried out by milling the HXNBR rubber inthe presence of water containing appropriate emulsifiers until therequired latex is formed. Suitable emulsifiers for this purpose includeamino emulsifiers such as fatty acid soaps, i.e., sodium and potassiumsalts of fatty acids, rosin acid salts, alkyl and aryl sulfonic acidsalts and the like. Oleate salts are mentioned by way of example. Therubber latex may be in solution in an organic solvent, or in admixturewith an organic solvent, when added to the water, to form anoil-in-water emulsion. The organic solvent is then removed from theemulsion to yield the required latex. Organic solvents that can be usedinclude the solvents that can be used for the hydrogenation reaction.

The invention is further illustrated in the following examples and inthe accompanying drawings. Of the drawings:

FIG. 1 is a graph showing the infrared spectrum of the polymer prior toand subsequent to hydrogenation; and

FIG. 2 is a graph showing the degree of hydrogenation achieved withdifferent amounts of ligand co-catalyst;

FIG. 3 is a graph showing the degree of hydrogenation of a polymer withtime using various different amounts of catalyst loading;

FIG. 4 is a bar chart showing die B tear strength of HNBR, XNBR andHXNBR compounds at different temperatures;

FIG. 5 is a bar chart showing die C tear strength of HNBR, XNBR andHXNBR compounds at different temperatures;

FIG. 6 is a bar chart showing the adhesion to nylon of HNBR, XNBR andHXNBR compounds at room temperature and at 125° C.;

FIG. 7 is a bar chart showing results obtained with HNBR, XNBR and HXNBRin the Pico abrasion test; and

FIG. 8 is a graph of storage tensile modulus E′ versus temperature forHNBR, XNBR and HXNBR.

SELECTIVE HYDROGENATION OF XNBR Example 1

In a lab experiment with a 6% polymer load, 184 g of a statisticalmethacrylic acid-acrylonitrile-butadiene terpolymer containing 28% byweight of acrylonitrile, 7% methacrylic acid, 65% butadiene, ML 1+4/100°C.=40(Krynac X 7.40, commercially available from Bayer), in 2.7 kg ofchlorobenzene was introduced into a 2 US gallon Parr high-pressurereactor. The reactor was degassed 3 times with pure H₂(100-200 psi)under full agitation. The temperature of the reactor was raised to 130°C. and a solution of 0.139 g (0.076 phr) oftris(triphenylphosphine)-rhodium-(I) chloride catalyst and 2.32 g ofco-catalyst triphenylphosphine (TPP) in 60 ml of monochlorobenzenehaving an oxygen content less than 5 ppm was then charged to the reactorunder hydrogen. The temperature was raised to 138° C. and the pressureof the reactor was set at 1200 psi (83 atm). The reaction temperatureand hydrogen pressures of the reactor were maintained constantthroughout the whole reaction. The degree of hydrogenation was monitoredby sampling after a certain reaction time followed by Fourier TransferInfra Red Spectroscopy (FTIR) analysis of the sample. Reaction wascarried out for 140 min at 138° C. under a hydrogen pressure of 83atmospheres. Thereafter the chlorobenzene was removed by the injectionof steam and the polymer was dried in an oven at 80° C. The degree ofhydrogenation was 95% (as determined by infrared spectroscopy and¹H-NMR). The FTIR result (FIG. 1) showed that the nitrile groups and thecarboxylic acid groups of the polymer remained intact after thehydrogenation, indicating the hydrogenation is selective towards the C═Cbonds only.

As can be seen, the peak for carbon-carbon double bonds has almostcompletely disappeared after hydrogenation, consistent with there being5% of residual double bonds. The peaks for the nitrile groups and forthe carbonyl group of the carboxyl group remain, indicating that therehas been no detectable reduction of nitrile and carboxyl groups.

The result of hydrogenation, together with results from Example 2, aresummarized in Table 1 below.

Example 2

Using Krynac X 7.40 as polymer and a catalyst concentration of 0.076%based on terpolymer weight in the polymer solution, hydrogenationreactions were carried out as in Example 1, in the presence of differentquantities of co-catalyst triphenylphosphine (TPP): i.e. 0-4% by weight,based on solid rubber, or co-catalyst/catalyst ratio of 0-53. FIG. 2 andTable 1 below shows the results of the hydrogenation. It is evident thatthe presence of a co-catalyst assists markedly in hydrogenation of thepolymer. Those runs with no co-catalyst are comparative and not inaccordance with the process aspect of the invention.

Table 1 Hydrogenation of XNBR (7.0% acid) with Different Ratios ofTriphenylphosphine (TPP) to Catalyst.

TABLE 1 Time (MIN) % hyd % RDB Time (MIN) % hyd % RDB Cat: 0.076 phr*,6% polymer, Cat: 0.076 phr, 6% Polymer, TPP: Cat. = 0:1 TPP: Cat. = 4:10 0 100 0 0 100 30 38.2 61.8 30 64.1 35.9 60 42.6 57.4 60 78.4 21.6 12043.6 56.4 120 86.5 13.5 180 43.1 56.9 180 87.9 12.1 240 88.6 11.4 Cat:0.076 phr, 6% polymer, Cat: 0.076 phr, 6% Polymer, TPP: Cat. = 16.7:1TPP: Cat. = 16.7:1 0 0 100 0 0 100 60 87.4 12.6 60 81.7 18.3 120 94.65.4 120 92.9 7.1 140 95.9 4.1 140 95 5 Cat: 0.076 phr, 6% polymer, Cat:0.076 phr, 6% Polymer, TPP: Cat. = 53:1 TPP/Cat . = 53:1 0 0 100 0 0 10030 71.4 28.6 30 68.6 31.4 60 83.9 16.1 60 86.2 13.8 120 94 6 120 93.86.2 180 96.7 3.3 180 96.6 3.4 240 97.8 2.2 240 97.3 2.7 300 98 2 *partsper 100 parts of rubber

Example 3

Further methacrylic-acrylonitrile-butadiene copolymers (7% acid, 28%ACN, 65% butadiene) were hydrogenated in accordance with the procedureof Example 1, but with different quantities of the catalyst ofExample 1. The degrees of hydrogenation achieved were in the range of 93to 99.5%. The results of these experiments are given in Table 2 andgraphically in FIG. 3.

Table 2 Hydrogenation of XNBR (7% Acid)

TABLE 2 Time (min) % Hyd % RDB Time (min) % Hyd % RDB 0.06 wt % Rh, 12%polymer, 0.096 wt % Rh, 12% polymer, TPP: cat. = 16.7:1 TPP: cat. =16.7:1 0 0 100 0 0 100 60 84.4 15.6 60 92.4 7.6 80 87.4 12.6 80 95.5 4.5120 90 10 120 97.2 2.8 180 92.3 7.7 180 98.7 1.3 240 93.1 6.9 240 99.30.7 300 99.7 0.3 0.06 wt % Rh, 12% polymer, 0.076 wt % Rh, 12% polymer,TPP: cat . = 16.7:1 TPP: cat. = 16.7:1 0 0 100 run 1 60 82.9 17.1 0 0100 80 87.5 12.5 60 81.7 18.3 120 90.6 9.4 120 92.9 7.1 180 93 7 140 955 240 94 6 run 2 0 0 100 60 87.4 12.6 120 94.6 5.4 140 95.9 4.1

Example 4

Following the procedure of Example 1, terpolymers of methacrylicacid-butadiene-nitrile with 3% acid and 3.5% acid monomer were subjectedto hydrogenation. Details and results are given in Table 3. It can beseen that with a 12% solution of polymer 0.076 phr of catalyst andco-catalyst ligand, in a ratio of catalyst to co-catalyst of 1:16.7,99+% hydrogenation was achieved in less than 2 hours.

Table 3. Hydrogenation Results for XNBR A and B 32% ACN and 3 and 3.5%Acid)

TABLE 3 Time (min) % hyd % RDB Time (min) % hyd % RDB A 12% polymer,0.076 phr cat. A 6% polymer, 0.05 phr cat. 0 0 100 0 0 100 30 83.5 16.534 69.9 30.1 60 94.4 5.6 60 81.6 18.4 120 98.9 1.1 90 88.9 11.1 180 99.50.5 120 92.4 7.6 135 94 6 150 95.1 4.9 B 12% polymer, 0.076 phr cat. B6% polymer, 0.05 phr cat. 0 0 100 0 0 100 30 82.7 17.3 35 67.6 32.4 6695.4 4.6 60 82.8 17.2 120 99.6 0.4 90 89.9 10.1 120 94.2 5.8 140 95.14.9

Example 5

Following the procedure of Example 1, hydrogenations of terpolymers offumaric acid-butadiene-acrylonitrile (<1% acid) were carried out.Without the use of a co-catalyst, 86% hydrogenation was achieved in 4hours. When a co-catalyst:catalyst ratio of 4:1 was used, 99%hydrogenation was achieved in 3 hours. The results are presented inTable 4.

Table 4. Hydrogenation of Fumaric Acid-Butadiene-Nitrile Terpolymer(0.076 phr Cat., 6% Polymer)

TABLE 4 0 TPP 0.3 phr TPP Time (min) % hyd % RDB Time (min) % hyd % RDB0 0.0 100.0 0 0 100 30 60.0 40.0 30 72.1 27.9 60 71.5 28.5 60 90.9 9.1120 82.0 18.0 120 98.5 1.5 180 84.6 15.4 180 99.5 0.5 240 86.0 14.0Physical Properties of HXNBR

The properties of the HXNBR of the invention were investigated in thefollowing examples. All non-polymer raw materials used in the examplesare commercially available. Preparative Examples 1 to 5 above werecarried out in the laboratory. The process was then transferred to apilot plant. The HXNBR that was subjected to testing for physicalproperties was made in the pilot plant but generally in accordance withthe conditions used in the laboratory. In particular, the amount ofcatalyst used was 0.076 phr, the weight ratio of triphenylphosphineco-catalyst to rhodium-containing catalyst was 16.7:1, the XNBRsubjected to hydrogenation was Krynac X 7.40 the solvent wasmonochlorobenzene and the solution was either 6% or 12% strength.

The HXNBR had a Mooney of 114 (ML 1+4 100° C.). The commerciallyavailable XNBR was Krynac X 7.40. Also used for comparison purposes wasa hydrogenated nitrile rubber (HNBR) commercially available from Bayerunder the trade-mark Therban C 3446, composed of 34% acrylontrile, 66%butadiene, hydrogenated to about 3.5-4.5% RDB. Therban C 3446 has aMooney of 58 (ML 1+4 100° C.).

Mixing Procedures

The HXNBR, HNBR and XNBR compounds were mixed in a 1.6 liter model BR82, Farrel Banbury mixer at 53 rpm. For better mixing, an 80% fillfactor was used when sizing the batch. The polymer was added first withcarbon black filler and mixed for about 1 minute followed by theaddition of all other dry fillers, stearic acid, non zinc containingantioxidants and plasticizer. The batch was dumped at a mixing time of 6minutes and the dump temperatures were recorded. In general the dumptemperature for HXNBR based compounds ranged between 140-155° C. For theother two polymer-based compounds, the dump temperature was below 140°C. Standard laboratory mill mixing procedures were used to incorporatethe curatives and zinc containing ingredients in a separate mixing step.

Example 6

In this example the compounds were subjected to peroxide curing. Theformulations of the HXNBR, HNBR and XNBR compounds are given in Table 5.

TABLE 5 Run A B C D E F CARBON BLACK, N660 50 50 50 50 50 50 HXNBR (5%RDB) 100 100 KRYNAC X7.40 100 100 THERBAN C 3446 100 100 NAUGARD 445 1 11 1 1 1 ANTIOXIDANT PLASTHALL TOTM 5 5 5 5 5 5 PLASTICIZER OIL STEARICACID 1 1 1 1 1 1 ACTIVATOR DIAK #7 CO-AGENT 1.5 1.5 1.5 1.5 1.5 1.5STRUKTOL ZP 1014 ZINC 7 7 7 PEROXIDE VULCUP 40KE ORGANIC 7.5 7.5 7.5 7.57.5 7.5 PEROXIDE VULKANOX ZMB-2/C5 0.4 0.4 0.4 0.4 0.4 0.4 (ZMMBI)ANTIOXIDANT ZINC OXIDE (KADOX 920) 3 3 3 ACTIVATOR Total 169.4 173.4169.4 173.4 169.4 173.4

The tensile strength, elongation at break, and modulus at differentstrains for these three compounds were tested at 23, 100, 125, 150 and170° C. Table 6 presents the tensile strength and elongation at breakfor HNBR, XNBR, and HXNBR compounds using ZnO activator. It is evidentthat the HXNBR based compound shows a physical property profile verydifferent from those of XNBR and HNBR.

When the samples were tested at room temperature, both XNBR and HXNBRshowed a higher modulus and higher tensile strength than those of HNBR.However, HXNBR based compound had a much better elongation at break thanthe XNBR based compound. HXNBR based compound also showed the besttensile strength and ultimate elongation at high testing temperature.

Table 6 Summary of Tensile Strength and Elongation at Break Results

TABLE 6 Compound No. A (HNBR) C (XNBR) E (HXNBR) Test Temperature (° C.)23 23 23 Hard. Shore A2 Inst. (pts.) 67 84 81 Ultimate Tensile (Mpa)23.63 25.66 29.3 Ultimate Elongation (%) 223 138 231 Test Temperature (°C.) 100 100 100 Hard. Shore A2 Inst. (pts.) 65 74 67 Ultimate Tensile(Mpa) 8.47 15.32 17.96 Ultimate Elongation (%) 109 116 329 TestTemperature (° C.) 125 125 125 Hard. Shore A2 Inst. (pts.) 65 76 66Ultimate Tensile (Mpa) 6.73 11.36 15.32 Ultimate Elongation (%) 95 100288 Test Temperature (° C.) 150 150 150 Hard. Shore A2 Inst. (pts.) 6566 67 Ultimate Tensile (Mpa) 6.46 10.03 13.21 Ultimate Elongation (%) 8789 257 Test Temperature (° C.) 170 170 170 Hard. Shore A2 Inst. (pts.)67 72 72 Ultimate Tensile (Mpa) 4.64 7.54 10.51 Ultimate Elongation (%)71 74 228Hot Tear Strength

Table 7 and FIGS. 4 and 5 compare the tear strength of HXNBR with thatof XNBR and HNBR at different testing temperatures. HXNBR showsexcellent tear strength at all temperatures in both die B and die C teartests. For example, when tested at 100 to 170° C., the die B tearstrength of HXNBR remains in the range of 30 to 40 kN/m, while the die Btear for XNBR and HNBR are only in the range of 10-20 kN/m (FIG. 4, andTable 7). In the case of die C tear test, although HXNBR shows the sametear strength as that of HNBR at room temperature, its tear strength istwo or three times that of HNBR at higher testing temperatures. The dieC tear strength of the HXNBR based compound is also much higher thanthat of the XNBR based compound in the temperature range 23 to 170° C.

Table 7 Tear strength in kN/m of HXNBR, XNBR and HNBR at DifferentTemperatures

TABLE 7 HNBR + HNBR + XNBR + XNBR + HXNBR + ZnO ZnO2 ZnO ZnO2 ZnOHXNBR + ZnO2 Die B  23° C. 46.95 40.69 50.73 43.74 85.45 62.18 100° C.16.26 15.09 23.51 21.41 39.76 31.65 125° C. 18.08 12.2 20.18 18.3 31.6325.01 150° C. 9.25 17.49 19.25 18.1 38.56 27.52 170° C. 11.02 10.5416.43 14.44 30.61 27.34 Die C  23° C. 32.46 34.45 23.51 20.42 32.2828.09 100° C. 11.25 11.03 10.77 7.23 21.74 20.37 125° C. 8.85 7.9 9.186.44 19.77 16.86 150° C. 4.57 5.5 6.79 5.12 16.22 14.11 170° C. 4.234.56 6.69 4.62 12.97 13.04Adhesion of HXNBR to Nylon Fabrics

One special property of HXNBR is improved adhesion to fabrics used inthe belt industry. This polymer shows excellent tear strength at hightemperature range and a better adhesion at high temperature. Theadhesion of HXNBR, XNBR and HNBR compounds to a nylon fabric (a nylonfabric commonly used in automotive timing belts) was tested at both 23and 125° C. The results of this test for the three compounds that usedZnO as activator are presented in Table 8 and FIG. 6.

It is evident that the adhesions of XNBR and HXNBR at room temperatureare better than that of HNBR. However, at 125° C. only HXNBR shows anadhesion that is as good as at room temperature. Both XNBR and HNBRbased compounds showed a significant decrease in adhesion strength whenthe testing temperature changed from 23 to 125° C.

Table 8 Adhesion Test Results at Different Temperatures

TABLE 8 Compound A (HNBR) C (XNBR) E (HXNBR) Cure Time (min) 40 40 40Cure Temperature (° C.) 160 160 160 Test Temperature (° C.) 23 23 23Adhesion To nylon nylon nylon Adhesive Strength (kNm) 2.92 3.62 4.97Cure Time (min) 40 40 40 Cure Temperature (° C.) 160 160 160 TestTemperature (° C.) 125 125 125 Adhesion To nylon nylon nylon AdhesiveStrength (kNm) 1.15 0.74 4.91Abrasion Resistance

It is known that the abrasion resistance of nitrile rubber (NBR) isimproved by introducing carboxylic acid groups into the polymer. Thiseffect is shown in Pico abrasion test (see FIG. 7). Although both HXNBRand XNBR show better abrasion resistance than the HNBR based compound,HXNBR based compound is far better than XNBR in abrasion resistance.This unique property of HXNBR demonstrates that this polymer has veryimportant potential in applications such as rubber rolls and shaftseals.

The superior abrasion resistance of HXNBR is not observed in the DINabrasion test as shown in Table 9. This is probably due to its ratherdifferent abrasion mechanism from the Pico abrasion test. In this test,both HNBR and HXNBR show better resistance to abrasion than the XNBRbased compound.

Table 9 DIN Abrasion Test Results

TABLE 9 A B C D E F HNBR HNBR XNBR XNBR HXNBR HXNBR Cure Time 25 25 2525 25 25 (min) Cure 170 170 170 170 170 170 Temper- ature (° C.)Specific 1.16 1.165 1.2 1.21 1.165 1.165 Gravity Abrasion 93 104 160 18192 96 Volume Loss (mm³)Cold Temperature Flexibility

The low temperature flexibility of HXNBR based compounds is comparedwith those of HNBR and XNBR based compound in both Gehman and TR tests.The results of these tests are summarized in Tables 10 and 11. Due tothe presence of 7% carboxylic acid groups, the low temperatureflexibility of HXNBR polymer is not as good as that of HNBR, as shown inboth TR and Gehman testing. The lower temperature properties of theHXNBR compounds are better to these of the XNBR compounds.

Table 10 Gehman Low Temperature Stiffness

TABLE 10 Compound No. A B C D E F HNBR HNBR XNBR XNBR HXNBR HXNBR CureTime 20 20 20 20 20 20 (min) Cure 170 170 170 170 170 170 Temper- ature(° C.) Start −70 −70 −70 −70 −70 −70 Temper- ature (min) Temper- −19 −19−2 −2 −3 −3 ature @ T2 (° C.) Temper- −24 −25 −11 −9 −15 −15 ature @ T5(° C.) Temper- −26 −26 −14 −13 −18 −19 ature @ T10 (° C.) Temper- −30−31 −24 −25 −28 −28 ature @ T100 (° C.)Table 11 Temperature Retraction Comparison

TABLE 11 Compound No. A B C D E F HNBR HNBR XNBR XNBR HXNBR HXNBR CureTime 20 20 20 20 20 20 (min) Cure 170 170 170 170 170 170 Temper- ature(° C.) Initial 50% 50% 50% 50% 50% 50% Elon- gation (%) TR 10 −22 −22−16 −14 −14 −14 (° C.) TR 30 −19 −19 −9 −8 −7 −8 (° C.) TR 50 −16 −16 −3−1 −2 −2 (° C.) TR 70 −13 −13 3 5 3 3 (° C.) Temp 9 9 19 19 17 17Retraction TR10- TR70

Example 7

Three peroxide-cured compounds were produced from HXNBR, a XNBR and aregular HNBR, using the following formulation shown in Table 12:

TABLE 12 Compound 4 5 6 CARBON BLACK, N 660 50 50 50 HXNBRC (J-11341)100 KRYNAC X7.40 100 THERBAN C 3446 100 NAUGARD 445 1 1 1 PLASTHALL TOTM5 5 5 STEARIC ACID 1 1 1 DIAK #7 1.5 1.5 1.5 STRUKTOL ZP 1014 7 7 7VULCUP 40KE 7.5 7.5 7.5 VULKANOX ZMB-2/C5 (ZMMBI) 0.4 0.4 0.4

The low temperature flexibility of these three compounds was determinedby using a Rheometrics Solid analyzer (RSA-II). In this test, a smallsinusoidal tensile deformation is imposed on the specimen at a givenfrequency. The resulting force, as well as the phase difference betweenthe imposed deformation and the response, are measured at varioustemperatures. Based on theory of linear viscoelasticity, the storagetensile modulus (E′), loss tensile modulus (E″) and tan δ can becalculated. In general, as the temperature decreases, rubber becomesmore rigid and, the E′ will increase. At close to the glass transitiontemperature, there will be a rapid increase in E′. FIG. 8 presents theE′-temperature plots for these three compounds. The HXNBR showed ahigher glass transition temperature than that of HNBR. It hassurprisingly been found that the glass transition temperature of HXNBRis lower than that of the XNBR.

1. A process for selectively hydrogenating carbon-carbon double bonds ofa polymer of a conjugated diene, an unsaturated nitrile and anunsaturated carboxylic acid, which comprises the steps of dissolving thepolymer in a solution which consists of an organic solvent and thensubjecting the polymer to hydrogenation in the presence of arhodium-containing compound as catalyst and a co-catalyst ligand,wherein the weight ratio of the rhodium-containing compound to theco-catalyst ligand is from 1:3 to 1:55, wherein the polymer comprisesfrom about 50 to about 85% conjugated diene, from about 15 to 50% ofunsaturated nitrile and from about 0.1 to 10% unsaturated carboxylicacid, and wherein an insignificant amount of nitrile and carboxylicacids groups are reduced during hydrogenation.
 2. A process according toclaim 1, wherein the rhodium-containing compound is a compound of theformula:(R_(m)B)_(i)RhX_(n) wherein each R is a C₁-C₆-alkyl group, aC₄-C₈cycloalkyl group, a C₆-C₁₅-aryl group or a C₇-C₁₅ aralkyl group, Bis an atom of phosphorus, arsenic or sulfur, or is a sulfonyl group S═O,X is hydrogen or an anion, I is 2, 3 or 4, m is 2 or 3 and n is 1, 2 or3.
 3. A process according to claim 1, wherein the co-catalyst ligand isof formula:R_(m)D where each R is a C₁-C₆-alkyl group, m is 2 or 3 and B is an atomof phosphorus, arsenic or sulfur, or is a sulfonyl group S═O.
 4. Aprocess according to claim 2, wherein B is phosphorus.
 5. A processaccording to claim 1, wherein the rhodium-containing compound istris-(triphenylphosphine)-rhodium(I)-chloride,tris-(triphenylphosphifle)-rhodium (III)Chloride,tris-(dimethyisulfoxide)-rhodium(III)-Chlorilde, ortetrakis-(triphenylphosphine)-rhodium hydride.
 6. A process according toclaim 1, wherein the amount of the rhodium-containing compound is in therange 0.03 to 0.5%, based on the weight of the polymer to behydrogenated.
 7. A process according to claim 4, wherein the co-catalystligand is triphenylphosphifle.
 8. A process according to claim 1,wherein the weight ratio of rhodium-containing compound to co-catalystligand is in the range 1:3 to 1:45.
 9. A process according to claim 1,wherein the amount of co-catalyst is in the range 0.1 to 33 parts byweight per hundred parts by weight of polymer.
 10. A process accordingto claim 9, wherein the amount of co-catalyst is in the range 0.5 to 20parts by weight per hundred parts by weight of polymer.
 11. A processaccording to claim 10, wherein the amount of co-catalyst is in the range1 to less than 5 parts by weight per hundred parts by weight of polymer.12. A process according to claim 1, wherein the amount of co-catalyst isgreater than 2 parts by weight per hundred parts by weight of polymer.13. A process according to claim 1, wherein the polymer that issubjected to selective hydrogenation has a molecular weight greater thanabout 60,000 (Mw).
 14. A process according to claim 2, wherein thepolymer that is subjected to selective hydrogenation has a molecularweight greater than about 100,000 (MW).
 15. A process according to claim1, which is carried out at a temperature in the range of 60 to 160° C.and a pressure in the range 10 to 250 atmospheres.
 16. A processaccording to claim 1, wherein the selective hydrogenation is carded outuntil at least 80% of the carbon-carbon double bonds have beenhydrogenated.
 17. A process according to claim 16, wherein the selectivehydrogenation is carried out until at least 90% of the carbon-carbondouble bonds have been hydrogenated.
 18. A process according to claim17, wherein the selective hydrogenation is carried out until at least95% of the carbon-carbon double bonds have been hydrogenated.
 19. Aprocess according to claim 18, wherein the selective hydrogenation iscarded out until at least 99% of the carbon-carbon double bonds havebeen hydrogenated.
 20. A process according to claim 1, wherein thepolymer comprises from 85 to 50% by weight of conjugated diene, from 0.1to 10% by weight of α,β-unsaturated carboxylic acid and from 15 to 50%by weight of acrylonitrile or methacrylonitrile.
 21. A process accordingto claim 1, wherein the conjugated diene is selected from the groupconsisting of 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene,3-pentadiene and piperylene.
 22. A process according to claim 21,wherein the conjugated diene is 1,3-butadiene.
 23. A process accordingto claim 1, wherein the nitrile is selected from the group consisting ofacrylonitdle, methacrylonitrile and α-chioroacrylonitrile.
 24. A processaccording to claim 23, wherein the nitrile is acrylonitrile.
 25. Aprocess according to claim 1, wherein α,β-unsaturated acid is selectedfrom the group consisting of acrylic acid, methacrylic acid, ethacrylicacid, crotonic acid, maleic acid, fumaric acid and itacoflic acid.
 26. Aprocess according to claim 1, wherein the α,β-unsaturated acid isselected from the group consisting of acrylic acid and methacrylic acid.